Diffusion research in HCP Mg-Al-Sn ternary alloys

Diffusion behavior in the HCP Mg-Al-Sn ternary alloys was experimentally investigated at 673 K and 723 K by analyzing solid-state diffusion couples. From the composition profiles analytically represented by error function expansion, the inter- and impurity diffusion coefficients were extracted by the Whittle-Green and generalized Hall methods respectively, which enable to establish the diffusion properties of the HCP Mg-Al-Sn alloys. The present results, together with the binary diffusion data of Mg-Al and Mg-Sn binaries, reveal that the average value of the main interdiffusion coefficient (D) over tilde (Mg)(SnSn), over the investigated compositions is 1.39 times larger than (D) over tilde (Mg)(AlAl) at 673 K and 1.36 times at 723 K, respectively, implying Sn diffuses comparably faster than Al in the HCP Mg-Al-Sn alloys. The main interdiffusion coefficients (D) over tilde (Mg)(AlAl) and (D) over tilde (Mg)(SnSn) and the impurity diffusion coefficient DSn(Mg-Al)* increases with increasing the content of diffusing element, either Al or Sn, however, DAl(Mg-Al)*increases first and then decreases as the Sn composition increases. The cross interdiffusion coefficients are scattering, their composition dependences are not very conclusive, however, a trend that (D) over tilde (Mg)(AlSn) and (D) over tilde (Mg)(SnAl) become negligibly small or even negative was evidenced as the content of Al or Sn approaches 0.